12v battery issues & replacement

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by sfwood, Apr 1, 2020.

  1. sfwood

    sfwood Junior Member

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    My 2012 Prius recently sat for over a week after which it wouldn't start. Found the 12v battery voltage to be below 7v. Bought a NOCO Genius 5 charger which got the battery up over 12v and allowed the car to start. Now the battery appears to max out at 12.5v and lose about 0.25v / day when the car isn't driven and the charger is removed. When the charger is left on the battery for "maintenance" it will, over the course of hours, charge up to the 4th and final (green) LED then drop back down to one or two red LEDs, repeating this cycle as long as the charger is attached. Some questions:
    __1) Seeing now that Toyoto recomends charging at 3.5 amps, is the NOCO Genius 5 too powerful for the Prius at 5 amps and if so what is a good charger for the Prius? The NOCO Genius 2 is much below 3.5.
    __2) Is there any reason to think it ISN'T time to replace this battery (original 2012 as far as I know)? My plan is to get a replacement from Toyota when it's reasonable to travel (they are an hour away).
    __3) In swapping out the battery for a new one, is hooking up a charger to the jump locations under the hood an acceptable way to maintain power to maintain computer memory?
    __Thanks very much for any advice!
     
  2. Raytheeagle

    Raytheeagle Senior Member

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    It sounds like it's 12 volt replacement time;).

    Good lick and stay safe in NEPA(y).
     
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  3. jzchen

    jzchen Senior Member

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    I found this while at a Costco one day, it was on sale at the time:


    https://www.costco.com/duracell-4-amp-battery-charger-and-maintainer.product.100479359.html

    If the battery is ever found that low in voltage, it should be replaced, per Toyota tech documents.

    Yes, you can put a charger on the jump points, just be careful when disconnecting the battery, in particular the positive pole. I’d immediately place the connection into a doubled zip lock bag...
     
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  4. sam spade 2

    sam spade 2 Senior Member

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    Yes. WAY past time for a new battery.
    I would NOT trust a charger connected while the battery is out.......because the voltage might spike up too high.
    I would also not worry about loosing any settings. It is often good to do a "cold boot".
     
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    It's more'n likely toast. If you want to see how toasty, and be more ready for the next time, look into electronic load testers, Solar BA9 is about $50~60 in the States.
     
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  6. bisco

    bisco cookie crumbler

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    auto parts and batteries plus stores have good ones if they are closer. no problem leaving the charger on the jump point
     
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  7. jzchen

    jzchen Senior Member

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    Regarding #2:

    Right after charging, (with the correct amp rated charger), turn on the high beams for 30 seconds. After turning them off measure the voltage at the battery posts. I can't recall the values, but I posted the instructions somewhere in this forum...

    moto g(7) power ?
     
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  8. 2012 Prius v wagon 3

    2012 Prius v wagon 3 Active Member

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    I would not worry about that at all. I'm curious to know if anyone has an actual answer to this, but I have noticed that virtually all car manufacturers put a similar, ridiculously low limit on charging, especially when the battery is inside the vehicle. Concern is probably due to a potential rare problem, and the lawyers make them say this - the workaround being to charge at an ultra low rate or remove the battery from the car while charging it at a normal rate.

    The thing is, though, that when the car itself is charging the battery, it puts FAR much more than that artificially low limit into the battery. So if one were to "jump-start" the 12V battery to get the car started, and let the car's DC-DC converter charge the 12V battery up to 14+V, as it does, it will be putting far more in there. I don't remember numbers, but I measured this with a clamp ammeter when figuring things out on my car soon after getting it. On normal cars, with 100+ Amp alternators, it is very common to put 100+ Amps into the battery, charging it up after sitting for a while and starting the engine. And those same cars will have similar excessively protective procedures for external charging - e.g., remove battery.

    I don't think anyone will try to talk you out of that. Mine is a 2012 as well. Got it last September. In trying to optimize my cars+batteries, I swapped in an Optima battery I had in a rarely used car, putting the Prius battery in that other car. Worked fine, and then when a deal came up, I bought a nice new AGM for that other car, turning in the Prius battery for the core deposit, even though it was working and testing just fine as I could tell.

    Regarding figuring out if your existing battery is any good, you will find parts stores with their magic machines the size of a voltmeter that do a test for 25 milliseconds and give you their answer. Other interweb people will give you a table of voltage measurements (a static test, with absolutely no test conditions specified, BTW, which may be a clue to how useful it is), nicely color coded to red yellow and green.

    But the real factor that kills batteries towards the end of their life is something that takes some time. They lose their "capacity." You can't measure that in an instant, or even by waiting for 25 milliseconds. Capacity tells you how much charge can be stored. One way to test would be to put load on the battery and see how quickly the voltage drop (i.e., a test taking fractions of an hour, not milliseconds). Another way, if starting with a low / dead battery is to put a charger on it and see how much time it takes to charge. If your 7V battery can charge up to 12.6V in 10 minutes before the float starts, that is a good measurement that the battery capacity is deficient.


    As sam spade 2 mentioned above, there is a possibility that the charger will put out voltage pulses that may confuse or damage the car's electronics. I'm a pretty cautious guy that would rather lose my radio presets than risk creating an electronics problem that will haunt me forever. So I would not risk it. Many others will do it with no problems. So one factor to consider is what you're giving up by disconnecting the battery - radio presets or more? If you want the best of everything, you could use a spare battery (everyone has at least one of these, right?) to jumper to the fuse box jump port, and hook the charger to that spare battery. The spare battery will buffer any voltage spikes, while also maintaining voltage. Similarly, if you have a jump pack, that should effectively buffer it.
     
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  9. sfwood

    sfwood Junior Member

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    Thank you very much everyone for the education. Having found in the Prius manual the statement that 5 amps is the charging max I will stick with the NOCO Genius5 I have. And (as I don't have an extra battery sitting around) I will take the warnings given above about spiking voltage to heart and not connect the charger for the changeover. I know which radio stations I listen to. :~)

    My local options for replacements seem to be AutoCraft Platinum AGM S46B24R, 370 CCA (Advance Auto) or Duralast Platinum 46B24R-AGM, 410 CCA (AutoZone). AutoZone also has the Optima which seems to get less love these days so I was leaning toward dealer battery. [The other two are very high CCA compared to OEM battery, but maybe that doesn't matter..? --ignore--was comparing CCA to Ah. oops] Any of these to be recommended? Thanks again
     
    #9 sfwood, Apr 2, 2020
    Last edited: Apr 2, 2020
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  10. bisco

    bisco cookie crumbler

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    all good. high cca is a good think
     
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    I heard high CCA comes at a cost of lowered amp hours, is achieved with more but thinner plates. I don't really understand, but get the sense the OEM specs are the optimum.

    That said I went with Optima Yellow Top. Next time around I might go with a Canadian Tire option that is sim to OEM, but cheaper.
     
  12. jzchen

    jzchen Senior Member

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    The manual says 5 amps, but if you take a look at the actual Toyota battery it's label says something lower, 4.2 A max I believe.

    You can charge the battery at the proper amp rating by driving the car/turning on in READY mode. Turn the car off, high beams on for 30 secs, then measure battery voltage. (You'll just use the engine/fuel to do this)...

    moto g(7) power ?
     
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